66 research outputs found
HMcode-2020::Improved modelling of non-linear cosmological power spectra with baryonic feedback
We present an updated version of the HMcode augmented halo model that can be
used to make accurate predictions of the non-linear matter power spectrum over
a wide range of cosmologies. Major improvements include modelling of BAO
damping in the power spectrum and an updated treatment of massive neutrinos. We
fit our model to simulated power spectra and show that we can match the results
with an RMS error of 2.5 per cent across a range of cosmologies, scales , and redshifts . The error rarely exceeds 5 per
cent and never exceeds 16 per cent. The worst-case errors occur at ,
or for cosmologies with unusual dark-energy equations of state. This represents
a significant improvement over previous versions of HMcode, and over other
popular fitting functions, particularly for massive-neutrino cosmologies with
high neutrino mass. We also present a simple halo model that can be used to
model the impact of baryonic feedback on the power spectrum. This six-parameter
physical model includes gas expulsion by AGN feedback and encapsulates star
formation. By comparing this model to data from hydrodynamical simulations we
demonstrate that the power spectrum response to feedback is matched at the
per cent level for and . We also present a
single-parameter variant of this model, parametrized in terms of feedback
strength, which is only slightly less accurate. We make code available for our
non-linear and baryon models at https://github.com/alexander-mead/HMcode and it
is also available within CAMB and soon within CLASS.Comment: 17 pages, 5 figures, 4 appendices; v2 - matches accepted version, new
appendix with comparisons between HMcode and 6 different emulator
Evaluation of Pax6 Mutant Rat as a Model for Autism
Autism is a highly variable brain developmental disorder and has a strong genetic basis. Pax6 is a pivotal player in brain development and maintenance. It is expressed in embryonic and adult neural stem cells, in astrocytes in the entire central nervous system, and in neurons in the olfactory bulb, amygdala, thalamus, and cerebellum, functioning in highly context-dependent manners. We have recently reported that Pax6 heterozygous mutant (rSey2/+) rats with a spontaneous mutation in the Pax6 gene, show impaired prepulse inhibition (PPI). In the present study, we further examined behaviors of rSey2/+ rats and revealed that they exhibited abnormality in social interaction (more aggression and withdrawal) in addition to impairment in rearing activity and in fear-conditioned memory. Ultrasonic vocalization (USV) in rSey2+ rat pups was normal in male but abnormal in female. Moreover, treatment with clozapine successfully recovered the defects in sensorimotor gating function, but not in fear-conditioned memory. Taken together with our prior human genetic data and results in other literatures, rSey2/+ rats likely have some phenotypic components of autism
The Convex Geometry of Linear Inverse Problems
In applications throughout science and engineering one is often faced with
the challenge of solving an ill-posed inverse problem, where the number of
available measurements is smaller than the dimension of the model to be
estimated. However in many practical situations of interest, models are
constrained structurally so that they only have a few degrees of freedom
relative to their ambient dimension. This paper provides a general framework to
convert notions of simplicity into convex penalty functions, resulting in
convex optimization solutions to linear, underdetermined inverse problems. The
class of simple models considered are those formed as the sum of a few atoms
from some (possibly infinite) elementary atomic set; examples include
well-studied cases such as sparse vectors and low-rank matrices, as well as
several others including sums of a few permutations matrices, low-rank tensors,
orthogonal matrices, and atomic measures. The convex programming formulation is
based on minimizing the norm induced by the convex hull of the atomic set; this
norm is referred to as the atomic norm. The facial structure of the atomic norm
ball carries a number of favorable properties that are useful for recovering
simple models, and an analysis of the underlying convex geometry provides sharp
estimates of the number of generic measurements required for exact and robust
recovery of models from partial information. These estimates are based on
computing the Gaussian widths of tangent cones to the atomic norm ball. When
the atomic set has algebraic structure the resulting optimization problems can
be solved or approximated via semidefinite programming. The quality of these
approximations affects the number of measurements required for recovery. Thus
this work extends the catalog of simple models that can be recovered from
limited linear information via tractable convex programming
Overview of the instrumentation for the Dark Energy Spectroscopic Instrument
The Dark Energy Spectroscopic Instrument (DESI) embarked on an ambitious 5 yr survey in 2021 May to explore the nature of dark energy with spectroscopic measurements of 40 million galaxies and quasars. DESI will determine precise redshifts and employ the baryon acoustic oscillation method to measure distances from the nearby universe to beyond redshift z > 3.5, and employ redshift space distortions to measure the growth of structure and probe potential modifications to general relativity. We describe the significant instrumentation we developed to conduct the DESI survey. This includes: a wide-field, 3.°2 diameter prime-focus corrector; a focal plane system with 5020 fiber positioners on the 0.812 m diameter, aspheric focal surface; 10 continuous, high-efficiency fiber cable bundles that connect the focal plane to the spectrographs; and 10 identical spectrographs. Each spectrograph employs a pair of dichroics to split the light into three channels that together record the light from 360–980 nm with a spectral resolution that ranges from 2000–5000. We describe the science requirements, their connection to the technical requirements, the management of the project, and interfaces between subsystems. DESI was installed at the 4 m Mayall Telescope at Kitt Peak National Observatory and has achieved all of its performance goals. Some performance highlights include an rms positioner accuracy of better than 0.″1 and a median signal-to-noise ratio of 7 of the [O ii] doublet at 8 × 10−17 erg s−1 cm−2 in 1000 s for galaxies at z = 1.4–1.6. We conclude with additional highlights from the on-sky validation and commissioning, key successes, and lessons learned
An Improved Algorithm for Approximating the Radii of Point Sets
We consider the problem of computing the outer-radii of point sets. In this problem, we are given integers n; d; k where k d, and a set P of n points in R ats F , of max p2P d(p; F ), where d(p; F ) is the Euclidean distance between the point p and at F . Computing the radii of point sets is a fundamental problem in computational convexity with signi cantly many applications. The problem admits a polynomial time algorithm when the dimension d is constant [9]. Here we are interested in the general case when the dimension d is not xed and can be as large as n, where the problem becomes NP-hard even for k = 1
Constrained Minimum-k-Star Clustering and its application to the consolidation of farmland
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